Thermally conductive resin composition and thermally conductive sheet including the same

ABSTRACT

A thermally conductive resin composition containing (A1) a fluorine-based compound having one to two terminal SiH group(s), in which a content of molecules having two such groups is 60 to 100 mole %, (B1) a fluorine-based compound having one to two terminal alkenyl group(s), in which a content of molecules having two such groups is 60 to 100 mole %, (A2) a fluorine-based compound in which a content of molecules having two terminal SiH groups is 0 to 40 mole %, (B2) a fluorine-based compound in which a content of molecules having two terminal alkenyl groups is 0 to 40 mole %, and (C) a thermally conductive filler, and satisfying, in connection with the content of the fluorine-based compounds, relation of [(A1)+(B1)]/[(A2)+(B2)]=20/80 to 80/20, (A1)/(B1)=20/80 to 80/20, and (A2)/(B2)=20/80 to 80/20, as well as a thermally conductive sheet including the same are provided.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a thermally conductive sheet used as asheet or the like interposed between a heat generator and a heatradiator for efficiently conducting heat from the heat generator to theheat radiator, and to a thermally conductive resin composition forforming the same.

Description of the Background Art

A thermally conductive sheet has conventionally been arranged between aheat generator such as electronic components and a heat radiator (a heatradiating member or a cooling member), as means for efficientlydissipating heat generated in various apparatuses or electronic devicesto the outside. By interposing a thermally conductive sheet havingflexibility and high heat conduction performance, a heat generator and aheat radiator can be coupled to each other with good adhesive force,with the thermally conductive sheet high in heat conduction performancebeing interposed. Therefore, consequently, as compared with a case wherea thermally conductive sheet is not interposed, efficiency in heatconduction from a heat generator to a heat radiator can be improved.

Many of thermally conductive sheets currently commercially available ingeneral are silicone rubber sheets mainly composed of silicon. It hasbeen well known, however, that the thermally conductive sheet made ofsilicone rubber gives rise to a problem of pollution of a system due tovolatilization of a low-molecular-weight siloxane component contained inthe sheet. In addition, recently, in particular in a market forsemiconductor manufacturing apparatuses or for power devices, athermally conductive sheet which withstands use at a high temperature of200° C. or higher has been demanded, however, the thermally conductivesheet made of silicone rubber has currently been challenged by a problemalso of such heat resistance.

In order to solve the problems above, Japanese Patent Laying-Open No.2010-232535 has proposed use as a thermally conductive sheet (aheat-resistant heat radiation sheet), of a fluororubber sheet mainlycomposed of fluorine, which is obtained by causing reaction and curingof a mixture of liquid fluorinated polyether and a thermally conductivefiller.

SUMMARY OF THE INVENTION

According to the fluororubber sheet, as compared with the siliconerubber sheet mainly composed of silicon, heat resistance can generallybe improved. The conventional thermally conductive fluororubber sheet,however, has suffered the following problem.

Namely, in order to provide a thermally conductive sheet itself withhigh heat conduction performance, a relatively large amount of thermallyconductive filler should be contained. When a large amount of thermallyconductive filler is contained, however, correspondingly, hardness ofthe sheet becomes higher or tack (tackiness) of a sheet surface becomeslower. Such increase in hardness and lowering in surface tack both lowercontact performance (adhesion) with a heat generator and a heat radiatorarranged adjacent to the thermally conductive sheet, which becomes afactor for increase in thermal contact resistance. As thermal contactresistance is higher, performance of the thermally conductive sheetcannot sufficiently be exhibited in spite of high heat conductionperformance of the thermally conductive sheet itself, and goodefficiency in heat conduction from the heat generator to the heatradiator cannot be obtained.

Then, an object of the present invention is to provide a thermallyconductive resin composition capable of forming a fluorine-based, highlyheat-resistant thermally conductive sheet achieving both of good lowhardness and high surface tack even in a case of filling with athermally conductive filler at a high rate and hence exhibitingexcellent heat conduction efficiency, and a thermally conductive sheetformed thereof.

The present inventor has conducted various studies in order to solve theproblems above, found the following points, conducted further studies,and completed the present invention.

(1) When a fluorine-based compound pair forming a fluorine-based polymer(a rubber-like elastic body) exhibiting elastomer characteristics as aresult of curing reaction (cross-linking) is used alone as afluorine-based compound forming a binder for a fluorine-based thermallyconductive sheet (for example, as in Examples in Japanese PatentLaying-Open No. 2010-232535 described above), hardness of a sheetbecomes higher or tack of a sheet surface lowers in a case of fillingwith a thermally conductive filler at a high rate.

(2) On the other hand, when a fluorine-based compound pair forming afluorine-based polymer (a gel-like elastic body) exhibiting gelcharacteristics as a result of curing reaction is used alone as thefluorine-based compound forming a binder for a fluorine-based thermallyconductive sheet, sheet forming becomes difficult.

(3) In contrast, according to a thermally conductive resin compositionobtained by using both of a fluorine-based compound pair forming afluorine-based polymer (a rubber-like elastic body) exhibiting elastomercharacteristics as a result of curing reaction [fluorine-based compounds(A1) and (B1) which will be described later] and a fluorine-basedcompound pair forming a fluorine-based polymer (a gel-like elastic body)exhibiting gel characteristics as a result of curing reaction[fluorine-based compounds (A2) and (B2) which will be described later]at an appropriate ratio as the fluorine-based compound forming a binderfor a fluorine-based thermally conductive sheet and also by adjustingblending ratios (A1)/(B1) and (A2)/(B2) to appropriate prescribedratios, a thermally conductive sheet having high heat resistance andhaving good low hardness and high surface tack even in a case of fillingwith a thermally conductive filler at a high rate can be obtained.

It is noted that the “elastomer characteristics” herein refer to Shore Ahardness in a range from 20 to 40, which is measured in conformity withJIS K6253. In addition, the “gel characteristics” refer to a penetrationnumber in a range from 60 to 80, which is measured in conformity withJIS K2207.

Namely, the present invention provides a thermally conductive resincomposition, containing the following components:

(A1) a fluorine-based compound having a perfluoroalkyl ether structurein a main chain and one to two hydrosilyl group(s) at a moleculeterminal, in which a content of molecules having two hydrosilyl groupsis 60 to 100 mole %;

(B1) a fluorine-based compound having a perfluoroalkyl ether structurein a main chain and one to two alkenyl group(s) at a molecule terminal,in which a content of molecules having two alkenyl groups is 60 to 100mole %;

(A2) a fluorine-based compound having a perfluoroalkyl ether structurein a main chain and one to two hydrosilyl group(s) at a moleculeterminal, in which a content of molecules having two hydrosilyl groupsis 0 to 40 mole %;

(B2) a fluorine-based compound having a perfluoroalkyl ether structurein a main chain and one to two alkenyl group(s) at a molecule terminal,in which a content of molecules having two alkenyl groups is 0 to 40mole %; and

(C) a thermally conductive filler, and satisfying, in connection withthe content of the fluorine-based compounds (A1), (B1), (A2), and (B2),the following Equations [1] to [3][(A1)+(B1)]/[(A2)+(B2)]=20/80 to 80/20  [1](A1)/(B1)=20/80 to 80/20  [2](A2)/(B2)=20/80 to 80/20  [3].

Preferably, the thermally conductive resin composition according to thepresent invention further satisfies, in connection with the content ofthe fluorine-based compounds (A1), (B1), (A2), and (B2), the followingEquations [4] and [5](A1)/(B1)=20/80 to 40/60 or 60/40 to 80/20  [4](A2)/(B2)=20/80 to 40/60 or 60/40 to 80/20  [5].

The fluorine-based compounds (A1), (B1), (A2), and (B2) can be acompound having a main chain structure expressed with the followingFormula [6]

(where n is an integer from 1 to 10).

The alkenyl group which the fluorine-based compounds (B1) and (B2) haveis, for example, a vinyl group.

The thermally conductive resin composition according to the presentinvention can contain 50 to 500 parts by weight of the thermallyconductive filler (C) with respect to a total content of 100 parts byweight of the fluorine-based compounds (A1), (B1), (A2), and (B2).Preferably, the thermally conductive resin composition according to thepresent invention further contains (D) a platinum-group-based catalyst.

In addition, the present invention provides a thermally conductive sheetcomposed of a cured product of the thermally conductive resincomposition according to the present invention above. The thermallyconductive sheet according to the present invention typically exhibitsASKER C hardness not higher than 70 and surface tack not lower than 30gf (which is measured in conformity with JIS Z3284).

According to the present invention, a thermally conductive sheet havinghigh heat resistance and having both of good low hardness and highsurface tack even in a case of filling with a thermally conductivefiller at a high rate and hence exhibiting excellent heat conductionefficiency can be provided.

The thermally conductive sheet according to the present invention hashigh heat resistance and exhibits excellent heat conduction efficiency,and it can be used suitably as a thermally conductive sheet in a widevariety of fields including various apparatuses, electronic devices, andthe like. When a thermally conductive sheet according to the presentinvention is applied, for example, to a semiconductor manufacturingapparatus, a semiconductor manufacturing process can be performed in ahigh-temperature environment. Therefore, higher integration of an LSIowing to a smaller line width of a circuit and hence a semiconductordevice higher in performance can be realized.

A conventional Si-based LSI is approaching its theoretical performancelimit, and demands for a next-generation power semiconductor includingsuch a material as SiC, GaN, or diamond have been increasing. On theother hand, there have been few peripheral members adapting tooperability at high temperature of a next-generation powersemiconductor, and among others, there has been no thermally conductivesheet exhibiting sufficient heat resistance and heat conductionefficiency. The thermally conductive sheet according to the presentinvention can fulfill such demanded characteristics, and it can suitablybe employed also for a power device such as a next-generation powersemiconductor.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

<Thermally Conductive Resin Composition>

A thermally conductive resin composition according to the presentinvention is suitably used for forming a thermally conductive sheetinterposed between a heat generator and a heat radiator, for efficientlyconducting heat from the heat generator to the heat radiator, and itcontains the following components:

(A1) a fluorine-based compound having a perfluoroalkyl ether structurein a main chain and one to two hydrosilyl group(s) at a moleculeterminal, in which a content of molecules having two hydrosilyl groupsis 60 to 100 mole % [hereinafter also referred to as a “fluorine-basedcompound (A1)”];

(B1) a fluorine-based compound having a perfluoroalkyl ether structurein a main chain and one to two alkenyl group(s) at a molecule terminal,in which a content of molecules having two alkenyl groups is 60 to 100mole % [hereinafter also referred to as a “fluorine-based compound(B1)”];

(A2) a fluorine-based compound having a perfluoroalkyl ether structurein a main chain and one to two hydrosilyl group(s) at a moleculeterminal, in which a content of molecules having two hydrosilyl groupsis 0 to 40 mole % [hereinafter also referred to as a “fluorine-basedcompound (A2)”];

(B2) a fluorine-based compound having a perfluoroalkyl ether structurein a main chain and one to two alkenyl group(s) at a molecule terminal,in which a content of molecules having two alkenyl groups is 0 to 40mole % [hereinafter also referred to as a “fluorine-based compound(B2)”]; and

(C) a thermally conductive filler.

As described above, the fluorine-based compounds (A1) and (B1) are afluorine-based compound pair forming a fluorine-based polymer (arubber-like elastic body) exhibiting elastomer characteristics as aresult of curing (cross-linking) reaction, and the fluorine-basedcompounds (A2) and (B2) are a fluorine-based compound pair forming afluorine-based polymer (a gel-like elastic body) exhibiting gelcharacteristics as a result of curing reaction. According to the presentinvention, these fluorine-based compounds (A1), (B1), (A2), and (B2) areused together and they are contained in a thermally conductive resincomposition at a characteristic blending ratio, so that a thermallyconductive sheet having high heat resistance and having both of good lowhardness and high surface tack can be realized.

Here, attention should be paid to the fact that the present invention isnot simply based on a concept of adjustment of characteristics of athermally conductive sheet which is obtained by blending a cross-linkedproduct (A1)−(B1) exhibiting elastomer characteristics and across-linked product (A2)−(B2) exhibiting gel characteristics. Thethermally conductive resin composition according to the presentinvention does not contain as blended components, the cross-linkedproduct (A1)−(B1) and the cross-linked product (A2)−(B2) prepared inadvance but contains the fluorine-based compounds (A1), (B1), (A2), and(B2) in a state before cross-linking. Therefore, as a result ofcross-linking of the four types of fluorine-based compounds above invarious combination, a thermally conductive sheet formed of thethermally conductive resin composition contains as a binder, alsovarious types of cross-linked products (more varieties of cross-linkedproducts, taking into account also a polymer chain length and the like),other than the cross-linked products (A1)−(B1) and (A2)−(B2).

The present invention is characterized in that, while the presentinvention is premised on the concept that a fluorine-based compound pairforming a cross-linked product exhibiting elastomer characteristics ifonly such fluorine-based compounds are cross-linked with each other anda fluorine-based compound pair forming a cross-linked product exhibitinggel characteristics if only such fluorine-based compounds arecross-linked with each other are used together so that a thermallyconductive sheet having both of an advantage of the elastomercharacteristics and an advantage of the gel characteristics is obtained,a ratio of contents of the four types of fluorine-based compounds isappropriately controlled in order to realize a thermally conductivesheet having desired characteristics, taking into account that variouscross-linked products are generated at the time of sheet forming asdescribed above.

[1] Fluorine-Based Compound (A1)

The fluorine-based compound (A1) is a fluorine-based compound having aperfluoroalkyl ether structure in a main chain and one to two hydrosilylgroup(s) (SiH group(s)) at a molecule terminal, in which a content ofmolecules having two hydrosilyl groups is 60 to 100 mole % andpreferably 80 to 100 mole % (therefore, a content of molecules havingone hydrosilyl group is 0 to 40 mole % and preferably 0 to 20 mole %)and being capable of addition reaction with an alkenyl group of thefluorine-based compound (B1) and the fluorine-based compound (B2).

A main chain structure of the fluorine-based compound (A1) can beconstituted of a perfluoroxyalkylene unit and it is preferably astructure expressed with the following Formula [6]

(where n is an integer from 1 to 10).

A representative example of a compound suitably used as thefluorine-based compound (A1) is a hydrosilyl-group-terminalfluorine-based compound expressed with the following Formula [7]

In Formula [7], n represents the meaning the same as above. Z¹ is across-linked portion containing a hydrosilyl group and representsSi(H)(R¹)₂. Z² represents Si(H)(R²)₂ as in Z¹ in a molecule having twoterminal hydrosilyl groups, and represents Si(R³)₃ in a molecule havingone terminal hydrosilyl group.

R¹, R², and R³ above may be the same or different, and they are eachindependently a substituted or non-substituted monovalent hydrocarbongroup, which is exemplified by: an alkyl group such as a methyl group,an ethyl group, a propyl group, a butyl group, a pentyl group, and ahexyl group; an aryl group such as a phenyl group, a tolyl group, and axylyl group; a halogenated alkyl group such as a 3-chloropropyl groupand 3,3,3-trifluoropropyl group; and the like. R¹, R², and R³ arepreferably an alkyl group having carbon atom number from 1 to 5.

The fluorine-based compound (A1) preferably has viscosity from 1.5 to4.0 Pa·s, which is measured in conformity with JIS K7117-1.

A trade name “SIFEL 8370-A” or the like manufactured by Shin-EtsuChemical Co., Ltd. can suitably be used as the fluorine-based compound(A1) expressed with Formula [7].

[2] Fluorine-Based Compound (B1)

The fluorine-based compound (B1) is a fluorine-based compound having aperfluoroalkyl ether structure in a main chain and one to two alkenylgroup(s) at a molecule terminal, in which a content of molecules havingtwo alkenyl groups is 60 to 100 mole % and preferably 80 to 100 mole %(therefore, a content of molecules having one alkenyl group is 0 to 40mole % and preferably 0 to 20 mole %) and being capable of additionreaction with a hydrosilyl group of the fluorine-based compound (A1) andthe fluorine-based compound (A2).

A main chain structure of the fluorine-based compound (B1) can beconstituted of a perfluoroxyalkylene unit and it is preferably astructure expressed with Formula [6] above. In the fluorine-basedcompound (B1) as well, n in Formula [6] is an integer from 1 to 10. Thenumber of ns in the fluorine-based compound (B1) may be the same as ordifferent from the number of ns in the fluorine-based compound (A1).

A representative example of a compound suitably used as thefluorine-based compound (B1) is an alkenyl-group-terminal fluorine-basedcompound expressed with the following Formula [8]

In Formula [8], n represents the meaning the same as above. Z³ is across-linked portion containing an alkenyl group and represents Si(alkenyl group) (R⁴)₂. Z⁴ represents Si (alkenyl group) (R⁵)₂ as in Z³in a molecule having two terminal alkenyl groups and represents Si(R⁶)₃in a molecule having one terminal alkenyl group.

R⁴, R⁵, and R⁶ above may be the same or different, and they are eachindependently a substituted or non-substituted monovalent hydrocarbongroup, which is as exemplified for R¹, R², and R³ above. R⁴, R⁵, and R⁶are preferably an alkyl group having carbon atom number from 1 to 5.

The alkenyl group is normally exemplified by a group having carbon atomnumber from 2 to 8 and preferably approximately from 2 to 4, such as avinyl group, a methylvinyl group, an allyl group, a propenyl group, abutenyl group, a pentenyl group, a hexenyl group, and a heptenyl group,and among others, the vinyl group is preferred.

The fluorine-based compound (B1) preferably has viscosity from 1.5 to4.0 Pa·s, which is measured in conformity with JIS K7117-1.

A trade name “SIFEL 8370-B” or the like manufactured by Shin-EtsuChemical Co., Ltd. can suitably be used as the fluorine-based compound(B1) expressed with Formula [8].

[3] Fluorine-Based Compound (A2)

The fluorine-based compound (A2) is a fluorine-based compound having aperfluoroalkyl ether structure in a main chain and one to two hydrosilylgroup(s) (SiH group(s)) at a molecule terminal, in which a content ofmolecules having two hydrosilyl groups is 0 to 40 mole % and preferably20 to 40 mole % (therefore, a content of molecules having one hydrosilylgroup is 60 to 100 mole % and preferably 60 to 80 mole %) and beingcapable of addition reaction with an alkenyl group of the fluorine-basedcompound (B1) and the fluorine-based compound (B2).

A main chain structure of the fluorine-based compound (A2) can beconstituted of a perfluoroxyalkylene unit and it is preferably astructure expressed with Formula [6] above. In the fluorine-basedcompound (A2) as well, n in Formula [6] is an integer from 1 to 10. Thenumber of ns in the fluorine-based compound (A2) may be the same as ordifferent from the number of ns in the fluorine-based compound(s) (A1)and/or (B1).

A representative example of a compound suitably used as thefluorine-based compound (A2) is a hydrosilyl-group-terminalfluorine-based compound expressed with the following Formula [9]

In Formula [9], n represents the meaning the same as above. Z⁵ and Z⁶represent the meaning the same as Z¹ and Z² above, respectively.

The fluorine-based compound (A2) preferably has viscosity from 1.5 to500 Pa·s, which is measured in conformity with JIS K7117-1.

A trade name “SIFEL 3405-A”, “SIFEL 3505-A”, or the like manufactured byShin-Etsu Chemical Co., Ltd. can suitably be used as the fluorine-basedcompound (A2) expressed with Formula [9].

[4] Fluorine-Based Compound (B2)

The fluorine-based compound (B2) is a fluorine-based compound having aperfluoroalkyl ether structure in a main chain and one to two alkenylgroup(s) at a molecule terminal, in which a content of molecules havingtwo alkenyl groups is 0 to 40 mole % and preferably 20 to 40 mole %(therefore, a content of molecules having one alkenyl group is 60 to 100mole % and preferably 60 to 80 mole %) and being capable of additionreaction with a hydrosilyl group of the fluorine-based compound (A1) andthe fluorine-based compound (A2).

A main chain structure of the fluorine-based compound (B2) can beconstituted of a perfluoroxyalkylene unit and it is preferably astructure expressed with Formula [6] above. In the fluorine-basedcompound (B2) as well, n in Formula [6] is an integer from 1 to 10. Thenumber of ns in the fluorine-based compound (B2) may be the same as ordifferent from the number of ns in the fluorine-based compound(s) (A1),(B1), and/or (A2).

A representative example of a compound suitably used as thefluorine-based compound (B2) is an alkenyl-group-terminal fluorine-basedcompound expressed with the following Formula [10]

In Formula [10], n represents the meaning the same as above. Z⁷ and Z⁸represent the meaning the same as Z³ and Z⁴ above, respectively.Similarly to the fluorine-based compound (B1), the alkenyl group cannormally be a group having carbon atom number from 2 to 8 and preferablyapproximately from 2 to 4, such as a vinyl group, a methylvinyl group,an allyl group, a propenyl group, a butenyl group, a pentenyl group, ahexenyl group, and a heptenyl group, and among others, the vinyl groupis preferred. The alkenyl group in the fluorine-based compound (B2) maythe same as or different from the alkenyl group in the fluorine-basedcompound (B1).

The fluorine-based compound (B2) preferably has viscosity from 1.5 to500 Pa·s, which is measured in conformity with JIS K7117-1.

A trade name “SIFEL 3405-B”, “SIFEL 3505-B”, or the like manufactured byShin-Etsu Chemical Co., Ltd. can suitably be used as the fluorine-basedcompound (B2) expressed with Formula [10].

[5] Content of Fluorine-Based Compound

The thermally conductive resin composition according to the presentinvention satisfies, in connection with the content of thefluorine-based compounds (A1), (B1), (A2), and (B2), the followingEquations [1] to [3][(A1)+(B1)]/[(A2)+(B2)]=20/80 to 80/20  [1](A1)/(B1)=20/80 to 80/20  [2](A2)/(B2)=20/80 to 80/20  [3].

By blending the fluorine-based compounds (A1), (B1), (A2), and (B2) at aratio of contents satisfying Equations [1] to [3] above, a thermallyconductive sheet having high heat resistance and having both of good lowhardness and high surface tack even in a case of filling with thethermally conductive filler (C) at a high rate can be obtained.

In order to obtain better low hardness and high surface tack, a ratio ofcontents [(A1)+(B1)]/[(A2)+(B2)] is preferably not lower than 25/75 andmore preferably not lower than 30/70 and preferably not higher than75/25. The ratio of contents [(A1)+(B1)]/[(A2)+(B2)] can be, forexample, not higher than 70/30, not higher than 60/40, or around 50/50.When the ratio of contents [(A1)+(B1)]/[(A2)+(B2)] is lower than 20/80,forming into a thermally conductive sheet tends to be difficult. On theother hand, when the ratio of contents [(A1)+(B1)]/[(A2)+(B2)] exceeds80/20, hardness of the thermally conductive sheet may become high orsurface tack may become low.

In addition to Equation [1] above, by setting the ratios of contents(A1)/(B1) and (A2)/(B2) each within a range from 20/80 to 80/20 (whichsatisfy Equations [2] and [3] above), both of good low hardness and highsurface tack can be achieved. In order to obtain better low hardness,however, the ratios of contents (A1)/(B1) and (A2)/(B2) preferablysatisfy the following Equations [4] and [5](A1)/(B1)=20/80 to 40/60 or 60/40 to 80/20  [4](A2)/(B2)=20/80 to 40/60 or 60/40 to 80/20  [5].

Namely, by excessively blending any one of the fluorine-based compounds(A1) and (B1) with respect to the other and excessively blending any oneof the fluorine-based compounds (A2) and (B2) with respect to the otherso as to satisfy Equations [4] and [5] above, the excessivefluorine-based compound effectively functions so that low hardness ofthe thermally conductive sheet can be improved. It is noted that, if theexcess above is too much, that is, the ratio of contents (A1)/(B1) or(A2)/(B2) is lower than 20/80 or higher than 80/20, forming into athermally conductive sheet tends to be difficult even though Equation[1] above is satisfied.

It is noted that, since the excessive fluorine-based compound above isanalogous in molecular structure to a binder forming the thermallyconductive sheet, it is unlikely to bleed (or extremely less likely tobleed) even during use at a high temperature. Bleeding of a componentcontained in a sheet during use at a high temperature becomes a factorfor pollution of a system, however, the thermally conductive sheetaccording to the present invention is free from such a disadvantage andit is highly heat resistant also in this regard.

[6] Thermally Conductive Filler (C)

The thermally conductive filler (C) is not particularly restricted and agenerally used filler can be employed, which is specifically exemplifiedby aluminum oxide (Al₂O₃), crystalline silicon oxide (SiO₂), magnesiumoxide (MgO), beryllium oxide (BeO), zinc oxide (ZnO), silicon nitride(Si₃N₄), boron nitride (hexagonal BN or cubic BN), aluminum nitride(AlN), silicon carbide (SiC), carbon fibers, diamond, graphite, and thelike.

The thermally conductive filler (C) can be in a shape of a grain, aflake, a needle, or the like, however, it is preferably in a shape of agrain because filling at higher density can be carried out. The granularthermally conductive filler (C) has an average particle size, forexample, from 0.1 to 100 μm and preferably from 0.5 to 50 μm.

As the thermally conductive filler (C), one type of a thermallyconductive filler may be used alone or two or more types of thermallyconductive fillers may be used as being mixed. In addition, taking intoaccount high-density filling capability or the like, two or more typesof thermally conductive fillers different in average particle size canalso be mixed for use.

In the thermally conductive resin composition according to the presentinvention, the content of the thermally conductive filler (C) isnormally set to 50 to 500 parts by weight and preferably 100 to 400parts by weight with respect to the total content of 100 parts by weightof the fluorine-based compounds (A1), (B1), (A2), and (B2). According tothe present invention, even when the content of the thermally conductivefiller (C) is increased, for example, to about 200 to 500 parts byweight, a thermally conductive sheet having good low hardness and highsurface tack can be obtained. If the content of the thermally conductivefiller (C) is not less than 50 parts by weight, preferably not less than100 parts by weight, and further preferably not less than 250 parts byweight with respect to the total content of 100 parts by weight of thefluorine-based compounds, sufficient thermal conductivity performance ofthe thermally conductive sheet itself is likely to be obtained.Furthermore, if the content of the thermally conductive filler (C) isnot more than 500 parts by weight and preferably not more than 400 partsby weight with respect to the total content of 100 parts by weight ofthe fluorine-based compounds, formability into a thermally conductivesheet can sufficiently be ensured and increase in hardness of athermally conductive sheet due to extreme filling with a thermallyconductive filler can be suppressed.

[7] Platinum-Group-Based Catalyst (D)

The thermally conductive resin composition according to the presentinvention can contain a platinum-group-based catalyst (D) catalyzingcross-linking reaction (hydrosilylation) between a hydrosilyl group andan alkenyl group of fluorine-based compounds, and it normally contains aplatinum-group-based catalyst (D). For example, a platinum-basedcatalyst is preferably employed as the platinum-group-based catalyst(D). Examples of the platinum-based catalyst include: metal platinum;chloroplatinic acid; platinum chloride; platinum-olefin complex;platinum-alkenyl siloxane complex; platinum-carbonyl complex;platinum-phosphine complex; platinum-alcohol complex; a substance inwhich a carrier made of alumina, silica, carbon black, or the likecarries platinum; and the like.

A rhodium-based compound, a ruthenium-based compound, an iridium-basedcompound, and a palladium-based compound are exemplified as theplatinum-group-based catalysts other than the platinum-based catalyst.

A content of the platinum-group-based catalyst (D) is not particularlylimited so long as the content is an effective amount necessary forpromoting cross-linking and curing of the thermally conductive resincomposition, and it can be 0 to 10 parts by weight with respect to thetotal content of 100 parts by weight of the fluorine-based compounds(A1), (B1), (A2), and (B2). Typically, the content is approximately from0.1 to 1000 ppm with respect to the total content above.

[8] Other Blended Components

The thermally conductive resin composition according to the presentinvention can contain an anti-aging agent, an antioxidant, a flameretardant, a dispersant, a solvent, and the like, as necessary.

<Thermally Conductive Sheet>

The thermally conductive sheet according to the present invention can beobtained by sheet forming the thermally conductive resin compositionabove with a common method and cross-linking the thermally conductiveresin composition through heating during forming. A forming method canbe exemplified by press forming, injection molding, transfer molding,extrusion, and the like.

Though a thickness of the thermally conductive sheet is set asappropriate depending on applications or the like, the thickness isnormally set to about 0.05 to 3 mm and preferably about 0.1 to 1 mm.

Since the thermally conductive sheet according to the present inventionis formed of the thermally conductive resin composition according to thepresent invention above, it has high heat resistance and exhibits goodlow hardness and high surface tack. The thermally conductive sheetaccording to the present invention typically has ASKER C hardness nothigher than 70, and it can have ASKER C hardness further not higher than60 and further not higher than 50. In addition, typically, surface tackmeasured in conformity with JIS Z3284 is not lower than 30 gf, and itcan further be not lower than 50 gf and further be not lower than 70 gf.

EXAMPLES

Though the present invention will be described hereinafter in furtherdetail with reference to Examples, the present invention is not limitedto these Examples. A test method in an evaluation test conducted forthermally conductive sheets obtained in Examples and ComparativeExamples below is as follows.

(1) 10% Compressive Load

A columnar test piece having a diameter of 46.2 mm and a thickness (aheight) of 1.0 mm was cut from the obtained thermally conductive sheet,and a load value (25° C.) at the time when load was applied thereto withthe use of “AUTO GRAPH AG-500kND” manufactured by Shimadzu Corporation,to thereby compress the thickness by 10%, was measured. The “10%compressive load” refers to a physical property value serving as anindicator of hardness of the thermally conductive sheet, and hardness islower as 10% compressive load is lower.

(2) Hardness

Hardness of the thermally conductive sheet at 25° C. was measured withan ASKER C durometer manufactured by ASKER. In order to evaluate heatresistance of the thermally conductive sheet, hardness before and afterheat treatment (250° C., 5 hours) was measured and variation in hardnesswas checked.

(3) Surface Tack

Surface tack of the thermally conductive sheet was measured inconformity with JIS Z3284, specifically as follows. A thermallyconductive sheet having a thickness of 0.75 mm was set on a stage of atackiness tester (“Texture Analyzer TA-XT2” manufactured by TextureTechnologies Corp.) and a ball probe made of stainless steel of ¼ inch φwas pressed against the thermally conductive sheet under measurementconditions below. Thereafter, a maximum resistance value at the time ofpulling up by 2 mm was measured at 7 points within 10 minutes, and anaverage value thereof was calculated.

(Measurement Conditions)

Plate and probe temperature: 25° C.

Fall velocity: 0.2 mm/second

Entry depth: 0.1 mm

Load: 100 gf

Time of pressing: 10 seconds

Speed of pulling up: 0.2 mm/second

Distance of pulling up: 2 mm

(4) Heat Resistance

A test piece of 10 mm long, 10 mm wide, and 1.0 mm thick, which was cutfrom the thermally conductive sheet, was bonded onto a heat generatingsubstrate (an amount of heat generation: 45 W). A substrate with coolingmechanism, which was made of the same material as the heat generatingsubstrate above, was arranged on the test piece, and the substrates werepressure-bonded to each other under constant load of 98 kPa. Atemperature sensor was attached to the substrates, and electric powerwas fed to the heat generating substrate while a temperature of thesubstrates was monitored. A temperature T₁ (° C.) of the heat generatingsubstrate and a temperature T₂ (° C.) of the substrate with coolingmechanism after lapse of 5 minutes since start of electric power feedwere measured, and heat resistance was calculated based on an equationbelowHeat Resistance (° C/W)=(T ₁ −T ₂)/Q[where Q represents an amount of heat generation (W) of the heatgenerating substrate]. In order to evaluate heat resistance of thethermally conductive sheet, heat resistance before and after heattreatment (250° C., 5 hours) was measured and variation in heatresistance was checked.

(5) Rate of Weight Reduction

Thermogravimetric (TG) analysis was conducted with the use of “TG-DTA6200” manufactured by Seiko Instruments Inc., and a rate of weightreduction due to heat treatment at 200° C. for 5 hours and a rate ofweight reduction (%) due to heat treatment at 250° C. for 5 hours weremeasured.

Examples 1 to 8, Comparative Examples 1 to 5

Each blended component shown in Tables 1 and 2 was mixed in an automaticmortar at a blending ratio shown in Tables 1 and 2 (a unit of a numericvalue being part by weight), and the mixture was caused to pass betweenrollers to achieve high dispersion. The obtained, kneaded product wasformed into a sheet through hot pressing (150° C., 10 minutes) by usinga mold. A thermally conductive sheet was thus fabricated. Details ofeach blended component used in Examples and Comparative Examples are asfollows.

[a] Fluorine-based compound (A1): a trade name “SIFEL 8370-A”manufactured by Shin-Etsu Chemical Co., Ltd. (a fluorine-based compoundin which a content of molecules having 2 hydrosilyl groups is within arange from 60 to 100 mole %)

[b] Fluorine-based compound (B1): a trade name “SIFEL 8370-B”manufactured by Shin-Etsu Chemical Co., Ltd. (a fluorine-based compoundin which a content of molecules having 2 alkenyl groups is within arange from 60 to 100 mole %)

[c] Fluorine-based compound (A2): a trade name “SIFEL 3405-A”manufactured by Shin-Etsu Chemical Co., Ltd. (a fluorine-based compoundin which a content of molecules having 2 hydrosilyl groups is within arange from 0 to 40 mole %)

[d] Fluorine-based compound (B2): a trade name “SIFEL 3405-B”manufactured by Shin-Etsu Chemical Co., Ltd. (a fluorine-based compoundin which a content of molecules having 2 alkenyl groups is within arange from 0 to 40 mole %)

[e] Silicon-based compound: “Sarcon” manufactured by Fuji PolymerIndustries Co., Ltd.

[f] Aluminum oxide A: “DAM-45” manufactured by Denki Kagaku KogyoKabushiki Kaisha (an average particle size of 40 μm)

[g] Aluminum oxide B: “DAM-05A” manufactured by Denki Kagaku KogyoKabushiki Kaisha (an average particle size of 0.5 μm)

[h] Platinum catalyst: “TEC10E50E” manufactured by Tanaka KikinzokuKogyo K.K. (a carried amount of 50 weight %)

TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6Example 7 Example 8 Binder Fluorine-Based Compound (A1) 30 25 35 15 4515 42 18 Fluorine-Based Compound (B1) 20 25 15 35 30 10 28 12Fluorine-Based Compound (A2) 30 25 35 15 15 45 18 42 Fluorine-BasedCompound (B2) 20 25 15 35 10 30 12 28 Silicon-Based Compound — — — — — —— — Total 100 100 100 100 100 100 100 100 [(A1) + (B1)]/[(A2) + (B2)]50/50 50/50 50/50 50/50 75/25 25/75 70/30 30/70 (A1)/(B1) 60/40 50/5070/30 30/70 60/40 60/40 60/40 60/40 (A2)/(B2) 60/40 50/50 70/30 30/7060/40 60/40 60/40 60/40 Thermally Aluminum Oxide A 270 270 270 270 270270 270 270 Conductive Filler (C) Aluminum Oxide B 30 30 30 30 30 30 3030 Platinum-Group- Platinum Catalyst 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5Based Catalyst (D) 10% Compressive Load (N/cm²) 37 87 45 60 75 40 80 38ASKER C Hardness Before Heat Treatment 51 68 48 52 61 50 63 47 AfterHeat Treatment 53 70 48 54 65 53 63 52 Surface Tack (gf) 72 52 68 65 3480 32 81 Heat Resistance Before Heat Treatment 3.5 4.5 3.7 4.0 6.1 3.16.3 3.0 (° C./W) After Heat Treatment 3.5 4.6 3.9 4.1 6.2 3.5 6.3 3.5Rate of Weight 200° C., 5 Hours 0.9 0.7 1.2 1.4 0.8 1.2 0.7 1.4Reduction (%) 250° C., 5 Hours 1.7 1.4 2.0 2.1 1.6 1.5 1.5 2.1

TABLE 2 Comparative Comparative Comparative Comparative ComparativeExample 1 Example 2 Example 3 Example 4 Example 5 Binder Fluorine-Based45 5 45 5 — Compound (A1) Fluorine-Based 5 45 45 5 — Compound (B1)Fluorine-Based 45 5 5 45 — Compound (A2) Fluorine-Based 5 45 5 45 —Compound (B2) Silicon-Based — — — — 100 Compound Total 100 100 100 100100 [(A1) + (B1)]/[(A2) + (B2)] 50/50 50/50 90/10 10/90 — (A1)/(B1)90/10 10/90 50/50 50/50 — (A2)/(B2) 90/10 10/90 50/50 50/50 — ThermallyConductive Aluminum Oxide A 400 270 270 270 425 Filler (C) AluminumOxide B 50 30 30 30 75 Platinum-Group-Based Platinum Catalyst 0.5 0.50.5 0.5 0.5 Catalyst (D) 10% Compressive Load (N/cm²) Sheet FormingSheet Forming 184 Sheet Forming 40 ASKER C Hardness Before HeatTreatment Not Achieved Not Achieved 96 Not Achieved 40 After HeatTreatment 99 54 Surface Tack (gf) 7 27 Heat Resistance (° C./W) BeforeHeat Treatment 5.7 1.6 After Heat Treatment 5.9 3.1 Rate of Weight 200°C., 5 Hours 1.0 0.7 Reduction (%) 250° C., 5 Hours 1.2 1.4

As shown in Table 1, it can be seen that the thermally conductive sheetsin Examples 1 to 8 were low in rate of change in hardness and heatresistance before and after heat treatment and also in rate of weightreduction, and therefore they had high heat resistance. In addition, thethermally conductive sheets in Examples 1 to 8 have good low hardness(ASKER C hardness not higher than 70) and high surface tack (not lowerthan 30 gf). Moreover, bleeding was not observed during heat treatment(250° C., 5 hours) of the thermally conductive sheets in Examples 1 to8.

In contrast, in Comparative Examples 1, 2, and 4, because (A1)/(B1) and(A2)/(B2) were excessively high or excessively low or[(A1)+(B1)]/[(A2)+(B2)] was excessively low, sheet forming could not beachieved. Furthermore, in the thermally conductive sheet in ComparativeExample 3, since [(A1)+(B1)]/[(A2)+(B2)] was excessively high, hardnesswas high and surface tack was also low.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the scopeof the present invention being interpreted by the terms of the appendedclaims.

What is claimed is:
 1. A thermally conductive sheet composed of a curedproduct of a thermally conductive resin composition, said thermallyconductive resin composition, comprising: A1) a fluorine-based compoundhaving a perfluoroalkyl ether structure in a main chain and one to twohydrosilyl group(s) at molecule terminal end of the main chain, in whicha content of molecules having two hydrosilyl groups is 60 to 100 mole %;(B1) a fluorine-based compound having a perfluoroalkyl ether structurein a main chain and one to two alkenyl group(s) at molecule terminal ofthe main chain, in which a content of molecules having two alkenylgroups is 60 to 100 mole %; (A2) a fluorine-based compound having aperfluoroalkyl ether structure in a main chain and one to two hydrosilylgroup(s) at molecule terminal end of the main chain, in which a contentof molecules having two hydrosilyl groups is 0 to 40 mole % while atotal content of molecules having one to two hydrosilyl group(s) is not0; (B2) a fluorine-based compound having a perfluoroalkyl etherstructure in a main chain and one to two alkenyl group(s) at moleculeterminal end of the main chain, in which a content of molecules havingtwo alkenyl groups is 0 to 40 mole % while a total content of moleculeshaving one to two alkenyl group(s) is not 0; and (C) a thermallyconductive filler, said thermally conductive resin compositionsatisfying, in connection with the content of said fluorine-basedcompounds (A1), (B1), (A2), and (B2), following Equations [1] to [3][(A1)+(B1)]/[(A2)+(B2)]=20/80 to 80/20 by weight  [1](A1)/(B1)=20/80 to 80/20 by weight  [2](A2)/(B2)=20/80 to 80/20 by weight  [3] wherein the ratio for equation(1) is based on a total weight of A1, B1, A2, and B2; the ratio forequation (2) is based on a total weight of A1 and B1; and the ratio forequation (3) is based on a total weight of A2 and B2; saidfluorine-based compounds (A1), (B1), (A2), and (B2) have aperfluoroalkyl ether structure in a main chain, wherein saidperfluoroalkyl ether structure is expressed with following Formula [6]

(where n is an integer from 1 to 10).
 2. The thermally conductive sheetaccording to claim 1, satisfying, in connection with the content of saidfluorine-based compounds (A1), (B1), (A2), and (B2), following Equations[4] and [5](A1)/(B1)=20/80 to 40/60 or 60/40 to 80/20 by weight  [4](A2)/(B2)=20/80 to 40/60 or 60/40 to 80/20 by weight  [5].
 3. Thethermally conductive sheet according to claim 1, wherein the alkenylgroup which said fluorine-based compounds (B1) and (B2) have is a vinylgroup.
 4. The thermally conductive sheet according to claim 1, whereinsaid thermally conductive resin composition comprises 50 to 500 parts byweight of said thermally conductive filler (C) with respect to a totalcontent of 100 parts by weight of said fluorine-based compounds (A1),(B1), (A2), and (B2).
 5. The thermally conductive sheet according toclaim 1, wherein said thermally conductive resin composition furthercomprises (D) a platinum-group-based catalyst.
 6. The thermallyconductive sheet according to claim 1, where said thermally conductivesheet has an ASKER C hardness not higher than 70 and a surface tack notlower than 30 gf, which is measured in conformity with JIS Z3284.